Process for obtaining a foamed ethylene polymer and product obtained thereby

ABSTRACT

A novel process is disclosed for the preparation of an ethylene polymer foam which is based on the use of a polycyclic polyene modified ethylene polymer, a sulfur based vulcanizing system and a foaming agent.

United States Patent Paiella et al.

[ Aug. 26, 1975 PROCESS FOR OBTAINING A FOAMED ETHYLENE POLYMER AND PRODUCT OBTAINED THEREBY Inventors: Roberto Paiella; Giampaolo Giuliani, both of San Donato Appl. No; 395,734

Foreign Application Priority Data Sept, 13, 1972 Italy 29239/72 U.S. CL. 260/25 HA; 260/795 C; 260/795 B;

260/8842 D Int. Cl. C08f 47/10 Field of Search 260/25 HA, 88.2 D

References Cited UNITED STATES PATENTS 10/1945 Alderson, .lr 260/25 HA Landler et a1 260/25 HA Alexander et 260/25 HA Patterson et al. 260/25 HA Hosoda et al. 260/25 HA Kawai et al. 260/25 HA Arrighetti et al. 260/882 D OTHER PUBLlCATlONS Werner Hoffman, vulcanization and Vulcanizing Agents," 1965, pp. 82-85.

Primary Examiner-Morton Foelak Attorney, Agent, or Firm-Ralph M. Watson, Esq.

ABSTRACT A novel process is disclosed for the preparation of an ethylene polymer foam which is based on the use of a polycyclic polyene modified ethylene polymer, a sulfur based vulcanizing system and a foaming agent.

5 Claims, No Drawings PROCESS FOR OBTAINING A FOAMED ETHYLENE POLYMER AND PRODUCT OBTAINED THEREBY The present invention refers to a process for producing foamed polyethylene and to the foamed polyethylene obtained thereby.

It is known that. among the thermoplastic polymers which are widely produced. polyethylene has never been employed remarkably in the cellular material field because it can difficultly be foamed as all the very crystalline polymers.

The foaming process is regularly performed up to obtain little and uniform cells only if the viscosity of the polymer mass has a suitable value, ranging within very narrow limits.

For instance it is very difficult to regulate the high density polyethylene viscosity by affecting the temperature owing to the fact. as soon as the melting tempera ture is exceeded, the polymer viscosity becomes very low and incompatible with a regular foaming process.

It is also known that many efforts have been performed in order to obtain foamed polyethylene by using cross-linking methods based on the employement of peroxide compounds or radiations. which remarkably affected the cost of the obtained product.

As a matter of fact the British Pat. No. 928.656 and the US. Pat. Nos. 3.098.831, 3.484.352 and 3.470.l l9

relate to methods for producing foamed polyethylene.

all of them providing the employment of peroxides and peculiar radiations in the polymer crossJinking phase.

It has now been found. that is an object of the present invention, it is possible to obtain foamed polyethylene, through a simple and economical way, by starting from a polyethylene containing a little percentage of unsaturations. in such a number that the characteristics of the starting polyethylene are unchanged. same being uni formly distributed along the polymer chain. which bl CH CH -CH 2 cross-link. before or during foaming. in presence of sulphur and accelerators base vulcanizing systems.

Foamcd polyethylene obtained according to the inventive process. a further object constitutes of. differentiates from the analogous product obtained according to the afore said methods.

The differences arise from the different type of latex and the cross bonds which. in our case. are constituted by sulphur bridges. whereas. in the other cases. the bond is between two carbon atoms belonging to two contiguous chains.

Practically this fact means that the products obtained according to the present process have a higher ductility and hence properties remarkably higher as to the tearing and abrasion resistance.

A further remarkable advantage is consisting of the possibility of co-vulcanizing the unsaturated polyethylencs of the present invention with unsaturated elastomers. preferably constituted by ethylene-propylenediene terpolymers. In such a way it is possible to produce foamed products having a flexibility variable with respect to the percentage of cowulcanizcd rubber.

The foaming process according to the present invention may be applied to any polyethylene containing unsaturations uniformly distributed along the macromolecular chain and able to vulcanize.

The unsaturations are particularly introduced into the polymer chain by eopolymerizing ethylene with variable amounts of a suitable comonomer consisting of a polycyclic polyene: in such a way a modified poly ethylene is obtained as described in Italian Patent No. 868.854. The comonomcr amounts in the polymer which is to be foamed range from 0.] to 10% by weight. According to the aforesaid patent the ethylene polymerization is carried out in presence of little amount of a polycyclic polyene having at least three double bonds in the molecule. preferably selected from the ones hereinafter listed:

dchydrodicyclopentadiene 2meth l-dehydrodicy clopenludiene Z-eyclopentadienyl-2 'norhorn- 5 -en lmethane norborn-S '-e nylmelhane (H -(H411 (2.6l-diullyl-dicyclopentadiene 2 allyl-tlicyclopentadiene -Continued iii) According to the inventive process it is possible to obi tain stiff foamed materials by starting from a polyethylene containing a very low percentage of unsaturations. which does not affect the intrinsic cristallinity of the polymer. and also more flexible foamed materials by using polyethylenes containing a higher percentage of unsaturations or copolymers formed by ethylene and an alpha-oleiine whose chain contains a low percentage of unsaturations.

The vulcanizing system employed is very vcrsatle and manageable and allows to regulate. within very wide ranges. the kinetics of cross-linking so that to make same to be the most possible compatible with the foam ing process and with the technology chosen for obtaining the foamed manufactured article.

The process for obtaining foamed polyethylene according to the present invention consists in adding the polymer the cross-linking agents (sulphur. ZnO. stcaric acid. accelerator. retarder. antioxidant) and the foaming agent (from l to parts per 100 parts of polymer) in a mixing roll at a temperature ranging from 100 to 140C. sufficiently high to allow the melting of polymer and hence the additives therein became homogeneous. but such that it does not allow the decomposition of the foaming agent or the polymer crossJinking The so ob tained mixture is then foamed according to methods well known to the man skilled in the art. Foamed polyethylene shows a cellular structure which is substan tially uniform. a density not higher than 0.3 g/cm. preferably comprised between (1.03 and 0.15 g/cm and at least 8571 of the pores lower than 1 mm. and on the av erage lower than 0.05 mm.

Moreover it shows a gel content ranging from 5 to 80%. preferably from to 50%. it being expressed as per cent of polymer insoluble in xylene at l( for 41) hours.

l -isopropylide n dicy elopentadiene l.J-dimeth lone9.h-endomelhylene' 1.4.5 .h.'-) l llhe\ahydronaphtalcnc l.4-dinietliylene-).fi-endomethylene 11.3.4 .5 1a.). 1 (l-octahydronaphtalene I.3-dimethylene-norborn-S -ene EXAMPLE l The following composition was homogenized in an open mixing roll at the temperature of C.

Polyethylene lM.F.l. 5)" 100 parts .-\.O.1Z4b l part ZnO 5 parts Stcaric acid 1 part NOBS special 1.5 parts Vulcacit DM [)5 part Sulphur 1.5 parts Avodicarbonannde 5 parts Polyethylene as ntodilied by introducing 1.2; of H or 5 :ncthyll) The mix was pressed at 180C and kg/cm pressure for 20. After such a time the pressure way removed and the material foamed.

The product had a (1.05 g/cm density, a fine and uniform cellular structure having 94% of closed cells.

On table 1 a comparison is made between some mechanical properties of a foamed eopolymer obtained according to what aforesaid and the ones of other materials which are imployed in the foamed polymers l'ield.

TABLE l** Material Density Closed Steam transmission Compression resistance glcm" cells gr/n in the foaming direction 7 kg/cm 24h 48h l20h 240h 5'); 10'; [5'4 20% FOAMEI) POLY- 0.063 943 8 118 28.2 50.1 7.44 7.78 8.1] 8.3l STYRENE FOAMED POLY- U 019 89.0 I 1.0] 15.3 61.5 l'llb 1.74 I 88 1.96 2.94 STYRENF. FOAMED POLY- 0.0]! 87.2 4l.38 KL! 1935 3TH! 0.52 0.70 0.71 0.77 URETHANF. FOAMED POLY- 0.054 93.8 3.1) 5.99 8.24 1304 [.86 l.9l L96 2.02 ETHYLENE* Material Compression resistance Compression Bending Abrasion in a direction perpendic- Modulus Modulus resistance ular to foaming one kg/cm kg/cm lCyele number kg/cm" necessary for foaming direction ahrading 5'7 ll)"; direcperpendicloll .tgr of tron ular one ntatterizlll FOAMED POLY 744 7.60 7.4l 7.]: 348 I958 340.8 75 STYRENE FOAMFD POLY- 2.0'. 1.93 I93 7.9 HHA 58.2 75.21 STYRENF. FOAMED POLY- 0.63 0.75 (1.78 0.83 24.6 In} [7.05 l5 URETHANE FOAMED POLY- L74 2.03 1.01 .04 49.5 52.7 (if-16 4000 ETHYLENE* See Example I All the measurements reported on the present lahli: were carried out according to methods set up in our laboratories EXAM PLE 2 The following composition was homogenized in an open mixing roll at the temperature of lC.

EXAMPLE 4 A composition similar to the one of example 2 was homogenized in a flat torpedo extruder and foamed at extruder output by passing the extruder material through an oven at high temperature (=C). The ex trusion temperatures were the following ones:

Polyethylene (M.F.l. 0.5)* 100 parts 35 A0. 2246 1 part Z 5 P Output 140C Stearlc LlCld l W" Central hody 160C NOBS Special 15 P Torpedo 100C Vulcacit DM 05 part Sulphur 1.5 parts 4 5 a t. 40 A foamed product was obtained at 0.l g/cm" density. Polyethylene was modified by introducing l.4'k of (4 or 5 methyll-Z- fine and uniform Ccllulfll Structure and clused eyelopentadienyl-2-norhorn-S enylmethane.

The mix was pressed at 180C and 140 kg/cm pressure for 20'. After such a time the pressure was removed and the material foamed. The product had a 0.09 g/cm density and a fine and uniform cellular structure having 9771 closed cells.

EXAMPLE 3 cells.

What we claim is: 1. A process for the production of a foamed ethylene polymer which comprises: a. forming a mixture of:

i. a copolymer of ethylene and from 0.1 to l0'7r by weight of a polycyclic polyene having at least three double bonds in the molecule;

ii. a sulfur based vulcanizing system; and

The following composition was homogenized in an iii. a foaming agent;

open mixing roll at the temperature of 135C. b. and foaming said mixture to form said foamed polyethylene. 2. A foamed ethylene polymer when obtained ac Polyethylene (M.F.l. l]" 100 parts A0 2246 1 pm cording to the process of claim V z o 5 parts 3. A process as defined in claim I wherein the polys cur a d I P cyclic polyene is (4 or 5 methyl)-2-cyclopentadienyl- NOBS SpCCtitl lpar b 1 Vulcucit DM 0.5 part -nor orn- -eny me an e. l Sulphur L5 parts 4. A process as defined in claim 1 wherein step (b) is Amd'cmmmmdc 3 carried out so that said foamed ethylene polymer has a Polyethylene was modified b introducing use of (4 or 5 methylI-Z- uniform cellular structure. a density ranging between 0.03 to 0.15 g/cm, at least 85% of the pores are not larger than I mm and a gel content ranging from 5 to S. A process as defined in claim I wherein the foaming agent is employed at from l to 15 parts per l00 parts of copolymer. 

1. A PROCESS FOR THE PRODUCTION OF A FOAMED ETHYLENE POLYMER WHICH COMPRISES: A. FORMING A MIXTURE OF: I. A COPOLYMER OF ETHYLENE AND FROM 0.1 TO 10% BY WEIGHT OF A POLYCYCLIC POLYENE HAVING AT LEAST THREE DOUBLE BONDS IN THE MOLECULE, II. A SULFUR BASED VULCANIZING SYSTEM, AND III. A FOAMING AGENT, B. AND FOAMING SAID MIXTURE TO FORM SAID FOAMED POLYETHYLENE.
 2. A foamed ethylene polymer when obtained according to the process of claim
 1. 3. A process as defined in claim 1 wherein the polycyclic polyene is (4 or 5 methyl)-2-cyclopentadienyl-2''-norborn-5''-enylmethane.
 4. A process as defined in claim 1 wherein step (b) is carried out so that said foamed ethylene polymer has a uniform cellular structure, a density ranging between 0.03 to 0.15 g/cm3, at least 85% of the pores are not larger than 1 mm and a gel content ranging from 5 to 80%.
 5. A process as defined in claim 1 wherein the foaming agent is employed at from 1 to 15 parts per 100 parts of copolymer. 